Production Of High-Pressure Gaseous Nitrogen

ABSTRACT

An improved process for producing elevated pressure nitrogen including providing an air separation unit with at least two columns. The process includes extracting a first nitrogen stream from the MP column, warming a first portion of the first nitrogen stream in a heat exchanger, thereby producing a product nitrogen stream, and warming a second portion of the nitrogen stream in the heat exchanger, thereby producing warm nitrogen stream. Expanding the warm nitrogen stream in an expander, thereby producing a quantity of work, and a low pressure nitrogen stream and introducing the low pressure nitrogen stream into the LP column. Extracting a second nitrogen stream from the LP column, cooling the second nitrogen stream in condenser, thereby producing a liquid nitrogen stream. Introducing a first portion of the liquid nitrogen stream into the LP column, increasing the pressure of a second portion of the liquid nitrogen stream, thereby producing a pressurized liquid nitrogen stream, and introducing a first portion of the pressurized liquid nitrogen stream into the MP column, and export a second portion of the pressurized liquid nitrogen stream as product.

FIELD OF INVENTION

The present invention relates to a process and an installation forproducing nitrogen under pressure.

BACKGROUND

In installations for producing nitrogen under pressure, the nitrogen isusually produced directly at the pressure of use, for example between 5and 10 bars. Purified air, compressed slightly above this pressure, isdistilled so as to produce the nitrogen at the top of the column and thereflux is achieved by expansion of the “rich liquid” (liquid at the baseof the column formed by air enriched with oxygen) and cooling of thecondenser at the top of the column by means of this expanded liquid. Therich liquid is thus vaporized at a pressure of between about 3 and 6bars.

If the size of the installation justifies this, the vaporized richliquid is passed through an expansion turbine so as to maintain theinstallation in the cold state but, often, this refrigerating productionis excessive, which corresponds to a loss of energy. In the oppositehypothesis, the cold state is maintained by an addition of liquidnitrogen coming from an exterior source, and the vaporized rich liquidis simply expanded in a valve and then travels through the thermalexchange line serving to cool the initial air. Consequently, here again,a part of the energy of the vaporized rich liquid is lost.

SUMMARY

The present invention is an improved process for producing elevatedpressure nitrogen including providing an air separation unit with atleast two columns. The process includes extracting a first nitrogenstream from the MP column, warming a first portion of the first nitrogenstream in a heat exchanger, thereby producing a product nitrogen stream,and warming a second portion of the nitrogen stream in the heatexchanger, thereby producing warm nitrogen stream. Expanding the warmnitrogen stream in an expander, thereby producing a quantity of work,and a low pressure nitrogen stream and introducing the low pressurenitrogen stream into the LP column. Extracting a second nitrogen streamfrom the LP column, cooling the second nitrogen stream in condenser,thereby producing a liquid nitrogen stream. Introducing a first portionof the liquid nitrogen stream into the LP column, increasing thepressure of a second portion of the liquid nitrogen stream, therebyproducing a pressurized liquid nitrogen stream, and introducing a firstportion of the pressurized liquid nitrogen stream into the MP column,and export a second portion of the pressurized liquid nitrogen stream asproduct.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a portion of one embodiment ofthe present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While theinvention is susceptible to various modifications and alternative forms,specific embodiments thereof have been shown by way of example in thedrawings and are herein described in detail. It should be understood,however, that the description herein of specific embodiments is notintended to limit the invention to the particular forms disclosed, buton the contrary, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the appended claims.

It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

Turning now to FIG. 1 that illustrates one embodiment of the presentinvention. Compressed, filtered, and pre-cooled air stream 101 entersmain heat exchanger 102 where it is cooled by indirect heat exchangewith at least streams 113 and 114, thus producing cooled air stream 103,which is then introduced into MP distillation column 104.

Rich liquid stream 105 is removed from the bottom of MP distillationcolumn 104, passed through auxiliary heat exchanger 106 where it issubcooled by indirect heat exchange with at least stream 109, therebyproducing cold rich liquid stream 107 which is then introduced into LPdistillation column 108. Cooling stream 109 exits the top of condenser110. After being in indirect heat exchange with rich liquid stream 105,cooling stream 109 is warmed, thereby producing warmed stream 111.

First nitrogen stream 112 is extracted from MP column 104 and split intoat least first nitrogen portion 113, second nitrogen portion 114, andthird nitrogen portion 115. First nitrogen portion 113 is warmed in mainheat exchanger 102, thereby producing product nitrogen stream 116.Optionally, product nitrogen stream 116 may be further compressed inproduct compressor 117, thereby producing pressurized product nitrogenstream 118. Second nitrogen portion 114 is warmed in main heat exchanger102, thereby producing warm nitrogen stream 119. Warm nitrogen stream119 is expanded in expander 120, thereby producing a quantity of work,and low pressure nitrogen stream 121, which is introduced into LPdistillation column 108. Third nitrogen portion 115 may be introducedinto LP column vaporizer 122, wherein it is condensed resulting incondensed nitrogen stream 132, which is introduced into MP column 104 asreflux.

Second nitrogen stream 123 is extracted from LP distillation column 108,and cooled in condenser 124, thereby producing liquid nitrogen stream125. Liquid nitrogen stream 125 is split into at least first liquidnitrogen portion 126 and second liquid nitrogen portion 127. Firstliquid nitrogen portion 126 is introduced into LP distillation column108. The pressure of second liquid nitrogen portion 127 is increased inpump 128 thereby producing pressurized liquid nitrogen stream 129.Pressurized liquid nitrogen stream is split into at least firstpressurized nitrogen portion 130 and second pressurized nitrogen portion131. First pressurized nitrogen portion 130 is introduced into MPdistillation column 108. Second pressurized nitrogen portion 131 isexported as product.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the invention.Accordingly, the protection sought herein is as set forth in the claimsbelow.

1. An improved process for producing elevated pressure nitrogen,comprising; providing an air separation unit with at least two columns,an LP column and an MP column, extracting a first nitrogen stream fromsaid MP column, warming a first nitrogen portion of said first nitrogenstream in a heat exchanger, thereby producing a product nitrogen stream,and warming a second nitrogen portion of said nitrogen stream in saidheat exchanger, thereby producing warm nitrogen stream, expanding saidwarm nitrogen stream in an expander, thereby producing a quantity ofwork, and a low pressure nitrogen stream, and introducing said lowpressure nitrogen stream into said LP column, extracting a secondnitrogen stream from said LP column, cooling said second nitrogen streamin condenser, thereby producing a liquid nitrogen stream, introducing afirst liquid nitrogen portion of said liquid nitrogen stream into saidLP column, increasing the pressure of a second liquid nitrogen portionof said liquid nitrogen stream, thereby producing a pressurized liquidnitrogen stream, and introducing a first pressurized nitrogen portion ofsaid pressurized liquid nitrogen stream into said MP column, and exporta second pressurized nitrogen portion of said pressurized liquidnitrogen stream as product.
 2. The process of claim 1, wherein a thirdnitrogen portion of said first nitrogen stream is introduced into an LPcolumn vaporizer.
 3. The process of claim 1, wherein said productnitrogen stream is further compressed in a product compressor, therebyproducing a pressurized product nitrogen stream.
 4. The process of claim1, further comprising: removing a rich liquid stream from said MPcolumn, removing a cooling stream from said nitrogen condenser,indirectly exchanging heat between said rich liquid stream and saidcooling stream, thereby producing a subcooled rich liquid stream whichis then introduced into said LP column.